int sys_fork ();
int sys_exec (int path, int argi);
int sys_riskexec (int path);
int sys_wait ();
int sys_dup (int fd);
int sys_open (int path);
int sys_read (int fd, int buf, int sz);
int sys_write (int fd, int buf, int sz);
int sys_close (int fd);
int sys_pipe (int fds);
int sys_exit ();
int sys_rm (int path);
int sys_ls (int buf);
int syscall (int n, int a0, int a1, int a2); 

#define SYS_FORK 0x0
#define SYS_RISKFORK 0x1
#define SYS_EXEC 0x2
#define SYS_WAIT 0x3
#define SYS_DUP 0x4
#define SYS_OPEN 0x5
#define SYS_PIPE 0x6
#define SYS_READ 0x7
#define SYS_WRITE 0x8
#define SYS_CLOSE 0x9
#define SYS_EXIT 0xA
#define SYS_RM 0xB
#define SYS_LS 0xC